First, I want to thank Labotka et al. for making me aware of their Kingston Peak Formation data in the Wildrose Canyon area, particularly the Sourdough Limestone Member (i.e., Bergfeld et al., 1996). I also want to thank Tony Fallick for patiently explaining to me the finer details of metamorphically driven C-isotope exchange, suggesting various ways to test C-isotope models, and pointing out the potential significance (see below) of the paper by Gibson et al. (1999). Second, I do not question the veracity of the Wildrose Canyon data. There, Labotka and colleagues conclude that isotopically light C was...